Method of recovering and reproducing substrates and method of producing semiconductor wafers

ABSTRACT

A method of recovering a first substrate, including the steps of: sticking a second substrate on a semiconductor layer epitaxially grown on the first substrate; and separating the semiconductor layer and the first substrate. Furthermore, a method of reproducing a first substrate, including the step of surface processing the first substrate separated. Furthermore, a method of reproducing a first substrate, including the step of homoepitaxially growing the first substrate surface processed. Furthermore, a method of producing a semiconductor wafer, including the step of epitaxially growing a semiconductor layer on a first substrate. Thus a group III nitride or similar, expensive substrate can be used to efficiently and economically, epitaxially grow a group III nitride or similar semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.10/895,142, filed on Jul. 21, 2004, claiming priority of Japanese PatentApplication No. 2003-291575, filed on Aug. 11, 2003, the entire contentsof each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods of efficientlyrecovering and reproducing substrates and methods of efficientlyproducing semiconductor wafers. More specifically, the present inventionrelates to methods of recovering and reproducing a first substratehaving a semiconductor layer formed thereon and methods of producingsemiconductor wafers including the steps of sticking a second substrateon the semiconductor layer and separating the first substrate from thesemiconductor layer.

2. Description of the Background Art

To grow a group III nitride semiconductor such asAl_(x)Ga_(y)In_(1-x-y)N, wherein 0≦x, 0≦y, and x+y≦1, a sapphiresubstrate is currently, generally used (see Group III NitrideSemiconductor, edited by Isamu Akasaki, Kabushiki Kaisha Baifukan, Dec.8, 1999, pp. 93-102, or Naoki Shibata, “Fabrication of LED Based onIII-V Nitride and its Applications”, Journal of the Japanese Associationfor Crystal Growth, JACG, vol. 29, No. 3, 2002, pp. 283-287). A sapphirecrystal and a group III nitride crystal, however, do not match inlattice constant, and to use a sapphire substrate to epitaxially grow agroup III nitride semiconductor layer it is necessary to initiallydeposit a group III amorphous layer on the sapphire substrate as alow-temperature deposited buffer layer and subsequently deposit thegroup III nitride semiconductor layer on the buffer layer, which resultsin reduced production efficiency.

If the above substrate is a group III nitride substrate, then the groupIII nitride semiconductor layer can epitaxially grown directly on thegroup III nitride substrate. (See S. Porowski et al., “Thermodynamicalproperties of III-V nitrides and crystal growth of GaN at high N₂pressure”, Journal of Crystal Growth 178, Elsevier Science B.V., 1997,pp. 174-188). The group III nitride substrate, however, is difficult togrow in liquid phase, and accordingly need to be grown in vapor phase.This cannot provide a large bulk crystal and is significantly costly.

SUMMARY OF THE INVENTION

The present invention contemplates a method of recovering andreproducing substrates and a method of producing semiconductor wafersthat allow a group III nitride or similar, expensive substrate to beused to efficiently and economically, epitaxially grow a group IIInitride or similar semiconductor layer.

The present invention in one aspect provides a method of recovering afirst substrate, including the steps of: sticking a second substrate ona semiconductor layer epitaxially grown on the first substrate and; andseparating the semiconductor layer and the first substrate.

The present invention in another aspect provides a method of reproducinga first substrate, including the steps of: sticking a second substrateon a semiconductor layer epitaxially grown on the first substrate;separating the semiconductor layer and the first substrate; andsurface-processing the first substrate separated. In addition to theabove steps the present method of reproducing the first substrate caninclude the step of homoepitaxially growing the first substratesurface-processed.

The present invention in still another aspect provides a method ofproducing a semiconductor wafer, including the steps of: sticking asecond substrate on a semiconductor layer epitaxially grown on a firstsubstrate; and separating the semiconductor layer and the firstsubstrate. In addition to the above steps the present method ofproducing the semiconductor wafer can include the steps of:surface-processing the first substrate separated; and epitaxiallygrowing a semiconductor layer on the first substrate surface-processed.Furthermore in addition to the above step the method can include thesteps of: surface-processing the first substrate separated;homoepitaxially growing the first substrate surface-processed; andepitaxially growing a semiconductor layer on the first substratehomoepitaxially grown.

Thus in accordance with the present invention the first substrate thatis expensive and poor in productivity can efficiently be recovered andreproduced and a semiconductor wafer can efficiently and economically beproduced.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in accordance with the present invention the step ofepitaxially grow a semiconductor layer on a first substrate.

FIG. 2 shows in accordance with the present invention the step ofsticking a second substrate on the semiconductor layer epitaxially grownon the first substrate.

FIG. 3 shows in accordance with the present invention the step ofseparating the semiconductor layer and the first substrate.

FIG. 4 shows in accordance with the present invention the step ofsurface-processing the first substrate separated.

FIG. 5 shows in accordance with the present invention the step ofepitaxially growing the first substrate having surface-processed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention in an embodiment will be described with referenceto the drawings specifically. In accordance with the present invention afirst substrate is recovered by a method in an embodiment, as follows.With reference to FIGS. 1 and 2, a first substrate 10 underlies anepitaxially grown semiconductor layer 11 and a second substrate 20 isstuck thereon. Then, with reference to FIG. 3, semiconductor substrate11 and the first substrate 10 are separated. Thus the first substratecan efficiently be recovered.

Herein, the first substrate 10 in the present invention refers to anexpensive substrate to be recovered, for example including a group IIInitride substrate formed of a group III nitride such asAl_(x)Ga_(y)In_(1-x-y)N, wherein 0≦x, 0≦y, and x+y≦1. The firstsubstrate is not particularly limited in thickness. When handleabilityis considered, however, the first substrate preferably has a thicknessof no less than 1.5 mm.

Semiconductor layer 11 epitaxially grown on the first substrate 10 isnot limited to a particular semiconductor layer 11. If the firstsubstrate 10 is a group III nitride substrate, however, thensemiconductor substrate 11 is implemented by a group III nitridesemiconductor formed of a group III nitride such asAl_(x)Ga_(y)In_(1-x-y)N and epitaxially grown, wherein 0≦x, 0≦y, andx+y≦1. Furthermore, semiconductor layer 11 is not limited to a singlesemiconductor layer and may be more than one semiconductor layerdeposited in layers.

How semiconductor layer 11 should epitaxially be grown is notparticularly limited. If the group III nitride semiconductor layer isepitaxially grown, it is preferably grown by metal organic chemicalvapor deposition (MOCVD), molecular beam epitaxy (MBE), hydride vaporphase epitaxy (HVPE) or the like.

The second substrate 20 refers to a substrate stuck on semiconductorlayer 11 and may be any general-purpose substrate suitable for stickingon semiconductor layer 11. The second substrate 20 preferably includes aSi substrate, an Al substrate, a Cu substrate, a Cu—W substrate, and thelike. The second substrate is not particularly limited in thickness.When handleability is considered, however, the second substratepreferably has a thickness of no less than 300 μm.

How the second substrate 20 is stuck on semiconductor layer 11 is notparticularly limited. Preferably, the second substrate 20 is brazed.More specifically, Ag, Ni, Au, Ge, Ti, an alloy thereof, or a similarwax is for example sputtered or vapor-deposited on semiconductor layer11 and then melted and the second substrate 20 is placed thereon andthus stuck together. Alternatively, a paste containing Ag, Ni, Au, Ge,Ti or an alloy thereof is applied on semiconductor layer 11 and thesecond substrate 20 is placed thereon and thus stuck together.

How semiconductor layer 11 and the first substrate 10 should beseparated is not particularly limited. Preferably, they are separatedfor example by using a wire saw or an inner, radial blade tomechanically slice the same, or electrolytically etching or similarly,chemically treating the same. In the electrolytical etching, for examplethe first substrate and the semiconductor layer with a conductive layerpreviously introduced therebetween are immersed in an electrolyte and acurrent is passed through the conductive layer to etch the conductivelayer to separate the first substrate and the semiconductor layer. Forexample if the first substrate is a group III nitride substrate and thesemiconductor layer is a group III nitride semiconductor layer, theconductive layer is formed of a group III nitride layer heavily dopedfor example with Si (and providing a specific resistance ofapproximately 10⁻² Ω·cm), and approximately 1N of aqueous KOH solutionis used with Pt corresponding to a negative electrode and the conductivelayer serving as a positive electrode and a current of approximately 1mA is passed to etch the conductive layer.

Desirably, semiconductor layer 11 and the first substrate 10 areseparated ideally at an interface of semiconductor layer 11 and thefirst substrate 10, as shown in FIG. 3. In that case ideally theintermediate product is separated into the second substrate 20 andsemiconductor layer 11 together forming a semiconductor wafer 30, andthe first substrate 10. In reality, however, a portion of the firstsubstrate can remain on semiconductor wafer 30 at a surface ofsemiconductor layer 11 (not shown) or a portion of the semiconductorlayer can remain on a surface of the first substrate 10 (not shown).Furthermore, if they are mechanically sliced and thus separated, it isdifficult to slice them at their interface, and if they are successfullysliced at the interface, semiconductor layer 11 is often damaged and hasa surface with protrusions and depressions, defects in crystallinity,and the like. Accordingly, in reality, to minimize damage tosemiconductor layer 11, a portion closer to the first substrate 10 thanthe interface of semiconductor layer 11 and the first substrate 10 isoften mechanically sliced. In that case, the intermediate product isseparated into the second substrate 20, semiconductor layer 11 and aportion of the first substrate 10 together forming a semiconductor wafer(not shown), and the remaining, first substrate 10. In the presentinvention, semiconductor wafer 30 and the first substrate 10 obtained byseparating semiconductor layer 11 and the first substrate 10 include anycase of the above.

In accordance with the present invention the first substrate isreproduced by a method in one embodiment, as follows: With reference toFIGS. 1 and 2, a first substrate 10 underlies an epitaxially grownsemiconductor layer 11 and a second substrate 20 is stuck thereon. Then,with reference to FIG. 3, semiconductor substrate 11 and the firstsubstrate 10 are separated. Then, with reference to FIG. 4, the firstsubstrate 10 separated is surface processed 40. Thus the first substratecan efficiently be reproduced.

The FIGS. 1-3 steps are as has been described above. Semiconductor layer11 and the first substrate 10 are separated and if the first substrate10 has a surface with protrusions and depressions or defective incrystallinity (not shown) or has a surface with the semiconductor layerpartially remaining thereon (not shown), then, with reference to FIG. 4,the first substrate 10 can be surface processed 40. How the firstsubstrate 10 should be surface processed is not particularly limited. Apolishing paper may be used to mechanically polish the substrate.Alternatively, polishing slurry and a polishing pad may be used tochemically, mechanically polish the substrate. Alternatively,liquid-phase etching, vapor-phase etching, or other similar chemicaltechniques may be employed. If the first substrate is a group IIInitride substrate and undergoes liquid-phase etching, the substrate isfor example brought into contact with etchant of a liquid at leastcontaining Na, Li or Ca.

In accordance with the present invention the first substrate isreproduced by the method in another embodiment, as follows: Withreference to FIGS. 1 and 2, the first substrate 10 underlies anepitaxially grown semiconductor substrate 11 and the second substrate 20is stuck thereon. Then, with reference to FIG. 3, semiconductor layer 11and the first substrate 10 are separated. Then, with reference to FIG.4, the first substrate 10 separated is surface-processed 40. Then, withreference to FIG. 5, the first substrate 10 surface processed ishomoepitaxially grown. In FIG. 5, the first substrate 10 a surfaceprocessed and thus reduced in thickness that is homoepitaxially grownprovides a homoepitaxially grown portion 10 b to provide the firstsubstrate 10 reproduced with its original thickness. Thus a firstsubstrate maintained in mechanical strength and excellent inhandleability can efficiently be reproduced.

The first substrate is homoepitaxially grown when the first substrate isreduced in thickness and hence mechanical strength and handleability.For example, if the first substrate is a group III nitride substrate,then preferably it is homoepitaxially grown when it attains a thicknessof no more than 0.6 mm. The homoepitaxial growth can be stopped when thefirst substrate recovers its original thickness or more.

How the first substrate 10 should homoepitaxially be grown is notparticularly limited. If the first substrate 10 is a group III nitridesubstrate, HVPE, MOCVD, MBE or the like is preferably employed.

In accordance with the present invention a semiconductor wafer isproduced by a method in an embodiment, as follows: With reference toFIGS. 1 and 2, the first substrate 10 underlies epitaxially grownsemiconductor layer 11 and the second substrate 20 is stuck thereon.Then, with reference to FIG. 3, semiconductor layer 11 and the firstsubstrate 10 are separated. Thus semiconductor wafer 30 can efficientlybe produced. Furthermore, by changing the second substrate 20 to bestuck, semiconductor wafer 30 having stuck thereto a substrateaccommodating the application of interest, can efficiently be produced.

Note that the first substrate 10 and semiconductor substrate 11 areseparated and if semiconductor wafer 30 obtained has semiconductor layer11 having a surface with a portion of the first substrate remainingthereon (not shown) or semiconductor layer 11 having a surface withprotrusions or depressions, defective in crystallinity, and/or the like(not shown), then a surface processing similar to surface processing 40applied to the first substrate 10 as described above can be performed.This processing is not limited to any particular method. A polishingpaper may be used to mechanically polish the substrate. Alternatively,polishing slurry and a polishing pad may be used to chemically,mechanically polish the substrate. Alternatively, liquid-phase etching,vapor-phase etching, or other similar chemical techniques may beemployed. If the first substrate is a group III nitride substrate andundergoes liquid-phase etching, the substrate is for example broughtinto contact with etchant of a liquid at least containing Na, Li or Ca.

In accordance with the present invention a semiconductor wafer isproduced by the method in another embodiment, as follows: With referenceto FIGS. 1 and 2, the first substrate 10 underlies an epitaxially grownsemiconductor substrate 11 and the second substrate 20 is stuck thereon.Then, with reference to FIG. 3, semiconductor layer 11 and the firstsubstrate 10 are separated. Then, with reference to FIG. 4, the firstsubstrate 10 separated is surface-processed 40. Then, with referenceagain to FIG. 1, a semiconductor layer 11 is epitaxially grown on thefirst substrate 10 surface processed. Thus the FIGS. 1-4 steps areperformed and the FIG. 1 step is then again formed. The steps cyclicallyperformed as described above allow semiconductor wafer 30 to be producedfurther efficiently.

In accordance with the present invention a semiconductor wafer isproduced by the method in still another embodiment, as follows: Withreference to FIGS. 1 and 2, the first substrate 10 underlies anepitaxially grown semiconductor substrate 11 and the second substrate 20is stuck thereon. Then, with reference to FIG. 3, semiconductor layer 11and the first substrate 10 are separated. Then, with reference to FIG.4, the first substrate 10 separated is surface-processed 40. Then, withreference to FIG. 5, the first substrate 10 surface processed ishomoepitaxially grown. Then, with reference again to FIG. 1, asemiconductor layer 11 is epitaxially grown on the first substrate 10homoepitaxially grown. Thus the FIGS. 1-5 steps are performed and theFIG. 1 step is then again formed. The steps cyclically performed asdescribed above allow semiconductor wafer 30 to be produced furtherefficiently.

The present invention will more specifically be described with referenceto examples.

First Example

With reference to FIG. 1, the first substrate 10 implemented by a groupIII nitride, GaN substrate having a thickness of 1.5 mm is used andMOCVD is employed to deposit semiconductor layer 11 on the GaN substrateheated to 1000° C. Semiconductor layer 11 is implemented by group IIInitride semiconductor layer formed of a p-GaN layer 111 having athickness of 150 nm, a p-Al_(0.2)Ga_(0.8)N layer 112 having a thicknessof 60 nm, an In_(0.2)Ga_(0.8)N layer 113 having a thickness of 3 nm, andan n-GaN layer 114 having a thickness of 5000 nm deposited successively.

Then, with reference to FIG. 2, on the semiconductor layer 111outermost, surface layer or n-GaN layer 114, Ag serving as a wax memberis sputtered and thus deposited and then melted and the second substrate20 implemented by a Si substrate having a thickness of 30 μm is stuckthereon. Then, with reference to FIG. 3, a wire saw is used to separatesemiconductor layer 111 and the first substrate 10. More specifically,although not shown, a portion of the first substrate that is 80 μmdistant from the interface of the semiconductor layer and the firstsubstrate is sliced with the wire saw parallel to the interface.

Then, with reference to FIG. 4, the first substrate 10 separated issurface-processed 40. More specifically, a liquid of Na serving asetchant is placed on the first substrate 10 or GaN substrate and asurface plate having a flat surface is pressed against the GaN substratewhile it is rotated at 50 rpm for one hour to perform liquid-phaseetching. Then, with reference to FIG. 5, the first substrate 10 or GaNsubstrate surface-processed to have a thickness of no more than 0.6 mmis heated to 1000° C., and HVPE is employed and GaN, the same materialas the GaN substrate, is used to homoepitaxially grow the substrate.When the GaN substrate recovers its original thickness, i.e., 1.5 mm,the homoepitaxial growth is terminated. Note that the substrate or thesemiconductor layer is controlled in thickness by the time required togrow the substrate or the semiconductor layer. More specifically, anexperiment is previously conducted to obtain a relationship between thetime required to grow the substrate or the semiconductor layer and itsthickness and for example a time required for growth is determined toallow the GaN substrate to have a thickness of 1.5 mm. The GaNsubstrate's thickness before the experiment and the growth can bemeasured with a film thickness meter of contact type. The result isshown in Table 1.

TABLE 1 1st Example 2nd Example 1st substrate Material GaN AlNEpitaxially growing the Method of MOCVD MOCVD semiconductor layerformation Chemical p-GaN(150)/p-Al_(0.2)Ga_(0.8)N(60)/p-GaN(150)/p-Al_(0.2)Ga_(0.8)N(60)/ Composition In_(0.2)Ga_(0.8)N(3)/n-In_(0.2)Ga_(0.8)N(3)/ (layer GaN(5000) n-GaN(5000) thickness: nm) 2ndsubstrate Material Si Cu Sticking the Method Brazed Brazed semiconductorsubstrate Material Ag Ni on the 2nd substrate (mole %) Separating theTool Wire saw Wire saw semiconductor layer and the 1st substrate Surfaceprocessing the Method Liquid-phase etching Liquid-phase etching 1stsubstrate separated Etchant Na Na Homoepitaxially Method HVPE HVPEgrowing the 1st Material GaN AlN substrate surface processed 3rd Example4th Example 1st substrate Material InN Al_(0.5)Ga_(0.5)N Epitaxiallygrowing the Method of MOCVD MOCVD semiconductor layer formation Chemicalp-GaN(150)/p-Al_(0.2)Ga_(0.8)N(60)/ p-GaN(150)/p-Al_(0.2)Ga_(0.8)N(60)/Composition In_(0.2)Ga_(0.8)N(3)/ In_(0.2)Ga_(0.8)N(3)/ (layern-GaN(5000) n-GaN(5000) thickness: nm) 2nd substrate Material Cu—W AlSticking the Method Brazed Brazed semiconductor substrate Material TiAu(50) on the 2nd substrate (mole %) Ge(50) Separating the Tool Inner,radial blade Inner, radial blade semiconductor layer and the 1stsubstrate Surface processing the Method Liquid-phase etchingLiquid-phase etching 1st substrate separated Etchant Na NaHomoepitaxially Method HVPE HVPE growing the 1st Material InNAl_(0.5)Ga_(0.5)N substrate surface processed

Second Example

Except that the first and second substrates are AlN and Cu substrates,respectively, the wax material is Ni, and the AlN substrate ishomoepitaxially grown with AlN used as material, the first substrate hasa semiconductor layer deposited thereon, the semiconductor layer has thesecond substrate stuck thereon, the semiconductor layer and the firstsubstrate are separated, the first substrate separated is surfaceprocessed and then homoepitaxially grown, similarly as has beendescribed in the first embodiment. The result is also shown in Table 1.

Third Embodiment

Except that the first and second substrates are InN and Cu—W substrates,respectively, the wax material is Ti, The semiconductor layer and thefirst substrate are separated with an inner, radial blade and the InNsubstrate is homoepitaxially grown with InN used as material, the firstsubstrate has a semiconductor layer deposited thereon, the semiconductorlayer has the second substrate stuck thereon, the semiconductor layerand the first substrate are separated, the first substrate separated issurface processed and then homoepitaxially grown, similarly as has beendescribed in the first embodiment. The result is also shown in Table 1.

Fourth Example

Except that the first and second substrates are Al_(0.5)Ga_(0.5)N and Alsubstrates, respectively, the wax member is Au (50 mole %)-Ge (50 mole%), the semiconductor layer and the first substrate are separated withan inner, radial blade, and the Al_(0.5)Ga_(0.5)N substrate ishomoepitaxially grown with Al_(0.5)Ga_(0.5)N used as material, the firstsubstrate has a semiconductor layer deposited thereon, the semiconductorlayer has the second substrate stuck thereon, the semiconductor layerand the first substrate are separated, the first substrate separated issurface processed and then homoepitaxially grown, similarly as has beendescribed in the first embodiment. The result is also shown in Table 1.

The present invention can recover and reproduce a group III nitride orsimilar, expensive substrate to form a cyclical semiconductor waferproduction process to efficiently and economically produce asemiconductor wafer having a group III nitride semiconductor layer orthe like.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1-6. (canceled)
 7. A method of recovering a first substrate, comprisingthe steps of: sticking a second substrate on a semiconductor layerepitaxially grown on said first substrate; and separating saidsemiconductor layer and said first substrate.
 8. A method of producing asemiconductor wafer, comprising the steps of: sticking a secondsubstrate on a semiconductor layer epitaxially grown on a firstsubstrate; and separating said semiconductor layer and said firstsubstrate.
 9. A method of recovering a first substrate formed of a groupIII nitride, comprising the steps of: epitaxially growing a firstsemiconductor layer on said first substrate; sticking a second substrateon said first semiconductor layer epitaxially grown on said firstsubstrate; and separating said first semiconductor layer and said firstsubstrate, the step of sticking including one of:sputtering/vapor-depositing a wax containing one of Ag, Ni, Au, Ge, Tiand an alloy thereof on said first semiconductor layer and then meltingsaid wax, and placing said second substrate thereon and thus stickingsaid second substrate together; and applying a paste containing one ofAg, Ni, Au, Ge, Ti and an alloy thereof on said first semiconductorlayer and placing said second substrate thereon and thus sticking saidsecond substrate together.
 10. A method of reproducing a first substrateformed of a group III nitride, comprising the steps of: epitaxiallygrowing a first semiconductor layer on said first substrate; sticking asecond substrate on said first semiconductor layer epitaxially grown onsaid first substrate; separating said first semiconductor layer and saidfirst substrate by mechanical slicing such that a portion of said firstsubstrate remains at a surface of said first semiconductor layer;surface-processing said first substrate separated from said firstsemiconductor layer after the step of separating; and homoepitaxiallygrowing a second semiconductor layer on said first substrate separatedfrom said first semiconductor layer when said first substrate is reducedin thickness to no more than 0.6 mrn after the step ofsurface-processed; wherein the step of surface-processing is performedby any of mechanical polishing, chemical-mechanical polishing,liquid-phase etching, and vapor-phase etching.